The invention relates to the monitoring of the quality of a communication channel supported by a sliding contact. It is known practice to transmit electrical signals between two mutually mobile elements. Such data transmission devices on a sliding contact are implemented in various fields.
A transmission device can for example comprise one or more slip rings and one or more respective contact elements, that will hereinafter be designated “wiper”: for example brushes, wires, fibers or similar, arranged so as to rub against the slip ring(s).
A communication channel involves a number of layers, including a physical layer, responsible for the actual transmission of signals, here electrical, here on a sliding contact, and other higher level layers. These higher level layers, called protocol layers in the present application, have various corresponding protocol parameters, notably parameters concerning a bit rate, a modulation, an error correcting code, a frame structure, communication rules (for example providing for the transmission of a frame to acknowledge reception and a repeat sending if a receipt acknowledgment frame is not received after a given time period), etc.
The invention thus has numerous applications, for example in medical imaging, crane systems, fairground rides, helicopters or wind turbines.
In particular, the invention will be applicable to signal transmission systems, or signal transfer systems (STS). These STS systems are electrical and mechanical systems whose function is to transmit, in an industrial machine, via a sliding contact, power electrical current and electrical signals, the latter transmission being performed according to a communication protocol.
Thus, in the case of a wind turbine, a slip ring device makes it possible to transfer data, notably between sensors installed on a mobile part of the nacelle, for example the nose of the nacelle of the wind turbine, and a processor in the nacelle or on the ground. For example, measurement data from sensors, for example values of blade orientation, of blade vibration, or similar, can be transmitted via this STS system, to the processor, and, conversely, control data from the processor, for example messages to impose a rotation of the blades, or similar, can also be transferred via the STS system.
Unfortunately, the quality of a communication channel implementing a sliding contact is likely to become degraded. This degradation is in all likelihood linked to a number of parameters, notably the temperature, the humidity, the presence of dust, the vibrations undergone, any overvoltages, etc.
It is known practice to regularly check, and if necessary improve, the state of the lubrications of the sliding contact in order to improve the quality of the transmissions. Nevertheless, such maintenance operations involving dismantling can be relatively complex and lengthy to perform, particularly when they involve an intervention at a location that is relatively difficult to access, like a wind turbine nacelle might be.
It is also known practice to detect the wear of a sliding contact from electrical measurements. The document FR 96 08944 thus describes a measurement of voltage and current on either side of a sliding contact. A resistance value is deduced therefrom and is compared to a threshold. If this resistance value is greater than the expected threshold, it is considered that the sliding contact is worn, and the contact is replaced.
The document US 2011/0309943 describes a method involving a monitoring of the useful signals received on one of the mobile elements and a statistical analysis of these signals.
It is however still relatively difficult to estimate whether a data communication protocol can be supported by a sliding contact in its current state.
There is therefore a need for a finer estimation of the quality of a communication channel implementing a signal transmission device between two mutually mobile elements.